It was a story about a girl who lived in a citadel and the world was about to be destroyed and she met a boy named Delos (I believe) but I don't remember her name. Not much to go on but I remember I loved this book when I was young and I have tried everything I can think of to look it up...
How about Skyborn by Marcia Krutchen?
From PaperBack Swap:
Clea is the grand-daughter of the King of Atlantic, but she is bored by her confortable life in the Citadel. Then a mysterious stranger arrives at the palace. Who is Delos, and why has he come? Is he connected with the plot against her grandfather? And what does the King mean when he says they are both Skyborn? In her search for the answers, Clea is caught up in a dangerously exciting adventure.